Reciprocating Compressor Vented Piston

ABSTRACT

A compressor ( 20 ) comprises: a case ( 22 ); and at least one piston ( 40 ) mounted for reciprocating movement, each in a respective cylinder ( 42 ) of the case. The at least one piston having a peripheral surface ( 50 ) and an upper surface ( 52 ), the upper surface having an outer portion ( 54 ) and a projection ( 80 ) extending from the upper surface. The at least one piston has a channel ( 220 ) positioned to pass flow from an area above the outer portion.

CROSS-REFERENCE TO RELATED APPLICATION

Benefit is claimed of U.S. Patent Application No. 62/210,108, filed Aug. 26, 2015, and entitled “Reciprocating Compressor Vented Piston”, the disclosure of which is incorporated by reference herein in its entirety as if set forth at length.

BACKGROUND

The disclosure relates to reciprocating compressors. More particularly, the disclosure relates to pistons.

Reciprocating compressors have long been used in applications such as refrigeration. One recent configuration involves pistons whose upper surface has a protrusion that, at top-dead-center, protrudes above the upper face of the cylinder block to help completely fill a volume within a valve plate to provide a more complete expulsion of compressed fluid.

SUMMARY

One aspect of the disclosure involves a compressor comprising: a case; and at least one piston mounted for reciprocating movement, each in a respective cylinder of the case. The at least one piston having a peripheral surface and an upper surface, the upper surface having an outer portion and a projection extending from the upper surface. The at least one piston has a channel positioned to pass flow from an area above the outer portion.

In one or more embodiments of any of the foregoing embodiments, the channel is a closed channel.

In one or more embodiments of any of the foregoing embodiments, the projection has an upper end and a central recess in the upper end and the channel has an upper end at the recess.

In one or more embodiments of any of the foregoing embodiments, the channel has a lower end along a side of the projection.

In one or more embodiments of any of the foregoing embodiments, the channel is one of a plurality of like channels distributed circumferentially about the at least one piston.

In one or more embodiments of any of the foregoing embodiments, the compressor comprises: a motor; a crankshaft driven by the motor; and at least one connecting rod coupling the crankshaft to the at least one piston.

In one or more embodiments of any of the foregoing embodiments, the projection has a frustoconical lateral surface.

In one or more embodiments of any of the foregoing embodiments, the channel comprises a drilled hole.

In one or more embodiments of any of the foregoing embodiments, the at least one piston comprises a plurality of identical pistons.

In one or more embodiments of any of the foregoing embodiments: the cylinder is formed in a cylinder block; a valve plate assembly is mounted to the cylinder block; and the at least one piston has a top-dead-center condition wherein the projection is at least partially within the valve plate assembly.

In one or more embodiments of any of the foregoing embodiments: the valve plate assembly has a seat forming a seating surface of a suction valve; and, in the top-dead-center condition, the projection is partially received within the seat.

In one or more embodiments of any of the foregoing embodiments: the seat forms an outer seating surface of a discharge valve; the valve plate assembly has an inner seat forming an inner seating surface of the discharge valve; the at least one piston has a recess in the projection; and, in the top-dead-center condition, the inner seat is partially received within the recess.

In one or more embodiments of any of the foregoing embodiments, a method for manufacturing the compressor comprises: drilling to form the channel.

In one or more embodiments of any of the foregoing embodiments, a method for using the compressor comprises: reciprocating the piston in the cylinder, during an upward portion of the reciprocating a flow of fluid moving upward in the channel.

In one or more embodiments of any of the foregoing embodiments, the flow of fluid is from a region adjacent a suction valve toward a discharge valve.

In one or more embodiments of any of the foregoing embodiments, a vapor compression system comprises the compressor.

In one or more embodiments of any of the foregoing embodiments, the vapor compression system is a refrigeration system.

The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a compressor.

FIG. 1A is an enlarged view of the forward-most two cylinders of the compressor of FIG. 1.

FIG. 1B is an enlarged view of a portion of the forward-most cylinder of the compressor of FIG. 1.

FIG. 2 is an isolated view of a piston of the compressor of FIG. 1.

FIG. 3 is an exploded cutaway view of a single cylinder of the compressor.

Like reference numbers and designations in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1 shows a compressor 20. The compressor has a case or housing assembly 22 which includes an inlet or suction port 24 and an outlet or discharge port 26. The exemplary compressor includes a motor 28 including a stator 32 and a rotor 30. The rotor 30 is integrated with a crankshaft 34 to drive rotation of the crankshaft about an axis 500. The crankshaft is supported by a plurality of bearings for rotation about the axis 500. The compressor is a reciprocating compressor having a plurality of pistons 40 mounted for reciprocal movement in respective associated cylinders 42 defined within a cylinder block 44 of the case. The exemplary cylinders are coupled to the crankshaft via wrist pins 46 carried by the pistons and connecting rods 48 coupling the wrist pins to the crankshaft.

Each piston has a lateral or side or outer diameter (OD) surface 50 (FIG. 1A) and an upper or top surface 52. FIG. 1A shows a forward-most piston in a top-dead-center (TDC) position. In the TDC position, a lateral portion 54 of the upper surface 52 is approximately flush to an upper surface 60 of the cylinder block 44. A valve plate assembly 70 is mounted atop the surface 60 (a gasket 62 intervening) and bears valve assemblies 72 associated with the respective cylinders. As is discussed further below, the valve assemblies 72 each comprise portions forming an inlet or suction valve and portions forming a discharge or outlet valve. A cylinder head 74 is mounted atop the valve plate assembly (a gasket 75 intervening) and encloses a discharge plenum 76 in communication with the discharge port 26.

FIG. 1A further shows the pistons comprising an upward projection 80 (having a lateral or side or outer diameter (OD) surface 82 and an upper or distal end 84) which, in the forward-most piston illustrated top-dead-center condition or position protrudes into the valve plate assembly 70. This helps minimize the headspace in the top-dead-center condition for improved overall flow.

The exemplary valve plate assembly 70 comprises a bottom plate 90 and a top plate 92 separated by spacers. The spacers may include a perimeter plate 94 matching the perimeter of the valve plate assembly so as to enclose a plenum 96. Additional spacers 98 may be distributed within the plenum. As is discussed further below, the plenum 96 is a suction plenum in communication with the suction port 24. For example, with the suction port 24 in a motor case section of the case assembly, the suction plenum 96 may be in communication with the interior of the motor case via a passageway (not shown) cast in the case assembly.

The suction valve comprises a flexible valve element 120 (FIG. 1B) mounted between the valve plate assembly 70 and cylinder block 44 at the periphery of each cylinder 42. The valve element 120 is formed as a sheet having a lower surface 122 and an upper surface 124. At each cylinder, the valve element has a central aperture defined by an inner perimeter (inner diameter (ID)) surface 126. In a closed condition, the upper surface 124 adjacent the inner perimeter 126 is seated against a seating surface 130 (an ID seat). The exemplary seating surface 130 is a lower surface of a seat 132 whose upper surface forms a discharge valve seating surface as is discussed further below. An inner diameter (ID) surface 134 of the seat closely accommodates the OD surface 82 of the projection 80 in the top-dead-center condition. An OD seating surface may be formed by a portion of the underside of the bottom plate 90.

The exemplary suction valve element is generally round but has two tabs 135 (FIG. 5) 180° apart that sit on the crankcase deck for support and two smaller tabs 136 serving as stops.

The exemplary seat 132 comprises an upper portion mounted to the upper plate 92 (e.g., via press fit, braze, or the like) and a lower portion depending through the plenum 96 and through an associated aperture 140 in the bottom plate 90. In operation, as the piston withdraws from its top-dead-center condition, reduced pressure/suction causes the valve element 120 to flex, bending in the middle (like a U) and supported by the two tabs 135 at the edge of the cylinder bore and stopped by cooperation of tabs 136 and complementary associated surfaces of recesses in the cylinder. This flexing downward disengages the element from the ID and OD seat surfaces to allow ingestion of refrigerant from the suction plenum 96 into the cylinder via a port 148 (an annular perimeter portion of the aperture 140 radially outboard of the outer diameter (OD) surface of the lower portion of the seat 132). Upon bottoming and reversing of the piston, the valve element 120 flexes back into its closed or sealing condition engaging the seating surfaces to close the port 148.

The discharge valve may similarly comprise a valve element 150 (FIG. 1B) which has an open condition and a closed condition. The exemplary valve element 150 is a spring-loaded annulus having a lower surface 152, an upper surface 154, an inner diameter (ID) perimeter surface 156, and an outer diameter (OD) perimeter surface 158. The exemplary seat for the valve comprises an inner diameter (ID) seat and an outer diameter (OD) seat. The outer diameter seat is formed by an upper seating surface 160 of the seat 132.

The exemplary ID seat is formed by an outer diameter perimeter surface 164 of an inner seat member 166. The member 166 is secured centrally to a valve guide 170 which, in turn, is mounted atop the upper plate 92. One or more springs 180 (e.g., a circumferential array of metallic coil springs held in pockets 182 in the guide (e.g., three to twenty such springs and pocket combinations per cylinder or eight to sixteen, with an exemplary twelve shown) may bias the valve element 152 into its closed condition.

As the piston moves upward towards its top-dead-center condition, eventually pressure in the headspace will exceed pressure in the discharge plenum. At this point (or thereafter due to bias of the discharge valve) the discharge valve element 150 will shift from its closed condition toward an open condition allowing refrigerant to pass from the headspace into the discharge plenum. When the piston reaches top-dead-center, the discharge valve will reclose.

With this exemplary configuration of discharge valve, the piston projection 80 includes a central recess 200 (FIG. 1A) that receives and accommodates the discharge valve inner seat member 166 as the piston approaches top-dead-center so as to minimize headspace.

As the piston approaches top-dead-center, gas in the small space above the lateral portion 54 of the upper surface 52 is driven upward. In a baseline system, this refrigerant is driven upward between the lateral surface 82 of the projection 80 and the adjacent ID surface 134 of the seat 132. The tightness of the space may cause flow resistance, reducing compressor efficiency. Accordingly, FIG. 1A adds channels 220 to a baseline piston configuration. The channels extend from lower ends 224 to upper ends 226. The lower ends may generally form inlet ports (inlets) and the upper ends 226 may generally form outlet ports (outlets) for flow to pass during that final stage of upward movement of the piston to the top-dead-center condition. The exemplary lower ends 224 are along the projection lateral surface 82; whereas, the exemplary upper ends 226 are along the recess 200. The exemplary channels 220 are closed channels (e.g., they have a full lateral perimeter) as distinguished from purely open channels or troughs. Accordingly, the exemplary channel 220 may be formed by drilling into the cast piston. An exemplary group of channels are evenly circumferentially distributed about the piston and cylinder axis 502. The exemplary configuration has four such channels 220 (FIG. 3). A broader range is 1-10 or 2-8.

During a late stage of upward movement, the channel lower end 224 will be exposed between the suction valve element above and piston upward surface lateral portion 52 below. Further upward movement of the piston will tend to drive some gas upward through the channel 220 exiting the upper end/outlet 226 and passing therefrom out the discharge valve. Tests on a prototype have shown approximately 1% improvement in efficiency at the rated condition of the baseline compressor. Depending upon implementation, embodiments may be configured to provide a slight increase in capacity (or potentially a slight decrease).

Exemplary dimensions of each hole involve a diameter of 0.5 mm and cross-sectional area of 4.9 mm². Exemplary aggregate cross-sectional area of the channels (e.g. four times the hole cross-sectional area for the exemplary piston) is 19.6 mm².

When compared to an otherwise similar baseline compressor lacking the holes/channels 220, the holes caused a TDC clearance volume increase of 5%. This would normally be expected to decrease overall performance. Nevertheless there was an observed performance increase due to the increased clearance volume's influence being outweighed by the improved flow, and reduced power. Thus, it is expected that a diminishing return on hole size flow benefit will be overcome by the increased clearance volume and cause decreased performance if the holes are too large. There may also be a lower threshold on hole size where small size does not provide overall benefit due to resistance to flow through the holes.

Alternative individual hole cross-sectional area is at least 2.0 mm² or 2.0 mm² to 10.0 mm². Alternative aggregate cross-sectional area is at least 5.0 mm² or 5.0 mm² to 50.0 mm².

An additional modification relative to the baseline compressor is the addition of vents 300 (FIG. 1B) to the spring pockets 182. In one exemplary modification, the baseline spring pocket is a blind bore extending upward from a lower perimeter surface portion 302 of the valve guide 170. The upper end of the baseline spring 180 sits against the base of the blind bore. The exemplary modification adds the vent 300 as a narrower passageway such as a drilled coaxial bore of smaller diameter leaving a shoulder 304 formed by a perimeter portion of the base surface of the baseline pocket. The vent 300 thus has a lower end 310 at the pocket 182 and an upper end 312 at an upper surface 314 of the valve guide 170.

One or more of several advantages may be obtained by adding the vent 300. Aspects of discharge valve responsiveness may be improved by allowing the pocket 182 to vent. For example, when the valve element 150 is driven upward from its closed position, vapor above the valve element is either driven into the pocket or squeezed laterally out through a peripheral opening 320. To the extent that vapor is driven into the pocket, this may cause back pressure in the pocket resisting upward movement of the valve element 150. To the extent that vapor is driven laterally outward, this may also involve back pressure but also may cause that vapor to compete with vapor displaced from the cylinder.

One or both of these situations may be addressed by addition of the vent. In some embodiments, the vent may allow vapor initially above the valve element 150 to be vented into the pocket and vapor in the pocket to be vented outward.

Yet an additional potential advantage of some embodiments involves passing of flow from the cylinder through the pocket and vent. For example, the nature of spring bias may be that during some portion or all of the discharging stroke of the piston, the valve element 150 does not top out and close the lower end of the pocket 182. In this situation, a portion of the vapor being discharged from the cylinder may pass radially and axially around the OD perimeter 160 of the valve element 150 and then back inward and upward through the pocket 182 and vent 300. In yet other situations, channels or other passageways may be provided so that flow may pass from the cylinder through the pockets and vents even with the valve element topped out against a stop surface.

Independently of the modifications discussed above regarding the piston channels 220, testing on a prototype showed a capacity increase of approximately 2% at the rating condition and an EER improvement of 1%.

Various further modifications may be made to the channels 220 or vents 300. In one example, the illustrated channels 220 may be replaced with fully open channels along the periphery of the projection or with some form of hybrid of open channel and closed channel such as an open channel along a lower portion of the projection periphery transitioning to a closed channel penetrating into the recess 200. Another variation might involve replacing the array of coil springs 180 and pockets 182 with a single wave spring (e.g., in an annular space such as a downwardly-open channel). The vents could extend upward from that annular space.

The compressor is used in a vapor compression system (e.g., refrigeration system including chillers, air conditioners, heat pumps, and the like). In such a system, the compressor may drive refrigerant flow along the recirculating flowpath passing through one or more heat rejection heat exchangers and one or more heat absorption heat exchangers. The basic configuration involves a sequential flowpath passing through a heat rejection heat exchanger, an expansion device, a heat absorption heat exchanger, and returning to the compressor.

The compressor may be made using otherwise conventional or yet-developed materials and techniques.

The use of “first”, “second”, and the like in the description and following claims is for differentiation within the claim only and does not necessarily indicate relative or absolute importance or temporal order. Similarly, the identification in a claim of one element as “first” (or the like) does not preclude such “first” element from identifying an element that is referred to as “second” (or the like) in another claim or in the description.

One or more embodiments have been described. Nevertheless, it will be understood that various modifications may be made. For example, when applied to an existing basic system, details of such configuration or its associated use may influence details of particular implementations. Accordingly, other embodiments are within the scope of the following claims. 

1. A compressor (20) comprising: a case (22); and at least one piston (40) mounted for reciprocating movement, each in a respective cylinder (42) of the case, the at least one piston having a peripheral surface (50) and an upper surface (52), the upper surface having an outer portion (54) and projection (80) extending from the upper surface, wherein the at least one piston has: a closed channel (220) positioned to pass flow from an area above the outer portion.
 2. (canceled)
 3. The compressor of claim 1 wherein: the projection has an upper end and a central recess (200) in the upper end; and the channel has an upper end (226) at the recess.
 4. The compressor of claim 1 wherein: the channel has a lower end (224) along a side of the projection.
 5. The compressor of claim 1 wherein: the channel is one of a plurality of like channels distributed circumferentially about the at least one piston.
 6. The compressor of claim 1 further comprising: a motor (28); a crankshaft (34) driven by the motor; and at least one connecting rod (48) coupling the crankshaft to the at least one piston.
 7. The compressor of claim 1 wherein: the projection has a frustoconical lateral surface (82).
 8. The compressor of claim 1 wherein: the channel comprises a drilled hole.
 9. The compressor of claim 1 wherein: the at least one piston comprises a plurality of identical pistons.
 10. The compressor of claim 1 wherein: the cylinder is formed in a cylinder block (44); a valve plate assembly (70) is mounted to the cylinder block; and the at least one piston has a top-dead-center condition wherein the projection is at least partially within the valve plate assembly.
 11. The compressor of claim 10 wherein: the valve plate assembly has a seat (132) forming a seating surface (130) of a suction valve; and in the top-dead-center condition, the projection is partially received within the seat.
 12. The compressor of claim 10 wherein: the seat forms an outer seating surface (160) of a discharge valve; the valve plate assembly has an inner seat (166) forming an inner seating surface (164) of the discharge valve; the at least one piston has a recess (200) in the projection; and in the top-dead-center condition, the inner seat is partially received within the recess.
 13. A method for manufacturing the compressor of claim 1, the method comprising: drilling to form the channel.
 14. A method for using the compressor of claim 1, the method comprising: reciprocating the at least one piston in the respective cylinder, during an upward portion of the reciprocating a flow of fluid moving upward in the channel.
 15. The method of claim 14 wherein: the flow of fluid is from a region adjacent a suction valve toward a discharge valve.
 16. A vapor compression system comprising the compressor of claim
 1. 17. The vapor compression system of claim 16 being a refrigeration system. 